TWI522172B - Process for the production of substitute natural gas - Google Patents

Description

Method for preparing alternative natural gas

The present invention relates to a process for preparing a fuel gas suitable for use as a substitute natural gas (SNG) from a synthesis gas produced from a partially oxidized carbonaceous fuel such as oil or coal.

Various methods are known for preparing SNG. One such method is described in US 4016189. Here, the feed gas is processed in a single high temperature large methanator and then processed in a single low temperature conditioning methanator. In this process, all new feed is added to a large methanator where a large amount of carbon dioxide is methanated to methane. Because the reaction is highly exothermic, thermal mass is required to limit the temperature rise in the bulk methanator to an acceptable level. The thermal mass is supplied as a recycle gas taken downstream of the large methanator but prior to conditioning the methanator. The recycle stream is compressed and then added upstream of the large methanator.

The single stage conditioning methanation reaction described in U.S. Patent 4,016,189 is suitable for the production of low heat producing gases having a 60% methane content. This is lower than the methane content required for current SNG product specifications.

It is well understood that large methanators typically receive some or all of the carbon monoxide-rich material (ie, new feed) fed to the plant. The methanator is adjusted to accept no new carbon monoxide feed and typically adjusts the methanation reaction at temperatures below that in a large methanator. For the purposes of the present invention, the recycle methanator is included in the recycle loop and does not accept new feeds rich in carbon monoxide.

Another method is suggested in US 4,205,961. The method is designed to optimize the plant's operating costs by reducing it. This can be achieved by reducing the number of large methanators. Specifically, the large methanation reaction load is split to two reactors. Fresh feed is added to both the first and second large methanators. The stream taken from the first large methanator is separated, a portion is recycled to the first large methanator via a compressor, and the remainder is passed to the second large methanator. The stream removed from the second large methanator is passed to the conditioning methanator.

The splitting of the load between the two large methanators essentially means less total overall load in the first large methanator. Since the recirculation is only carried out around the first large methanator, the recirculation flow rate need only be sufficient to control the temperature rise of the bed. This higher load means that there is less reaction heat that must be removed by the recycle gas, which then produces a lower recycle flow rate. The gas flowing forward from the first large methanator to the second large methanator acts as a thermal mass to quench the overall reaction of the second stage. In the flow chart described in U.S. Patent 4,205,961, about 70% of the fresh feed is passed to the first large methanator and the remainder to the second large methanator. The second large methanator has the effect of reducing the recycle flow rate by 30% while maintaining the same recycle loop pressure drop. This has the benefit of reducing the energy requirements of the recycle compressor, but at the expense of the second methanator reactor. The product gas produced by the process described in US 4,205,961 does not meet the requirements of current SNG specifications.

Various alternative methods are described in US 4,133,825. Unlike other methods in which the shift zone is included upstream of the methanation unit, the process described herein introduces the concept of shifting and methanating the feed gas over the methanation catalyst and methanation unit. This does result in excess carbon dioxide being present in the product and therefore requires the inclusion of a carbon dioxide removal unit downstream of the methanation unit. Performing this transformation in this methanation unit requires a large amount of steam. It is therefore proposed to include a saturator upstream of the methanation zone to simultaneously saturate and heat the feed stream with steam prior to bulk methanation. This not only provides the required steam for the shift reaction on the methanation catalyst but also prevents the formation of carbon on the catalyst.

In one configuration, two large methanators are used, with a portion of the feed flowing into the first large methanator and the remainder into the second large methanator. All of the removal from the first large methanator flows into the second large methanator and is recycled after the second large methanator. After flowing through the compressor, the recycle flows into the first large methanator. The portion of the second large methanator that is not used for recycling flows into the conditioning methanator. In another method, two or more large methanators are described and the feedstock feed is split between all of the large methanators present. This recycle is then taken after the final large methanator.

Performing a shift reaction within the methanation unit eliminates the need for individual transform regions. However, as the flow rate through the methanation unit is greater and there is a large amount of carbon dioxide that does not undergo any reaction from the feed to the product, the amount of catalyst required increases and the size of all equipment items other than the compressor increases. . This is because carbon dioxide provides a large thermal mass for removing heat from the overall system, and thus does not require large recirculation.

Another method is described in US 4,298,694. In this process, a dual catalyst is used to reduce the operating cost of the SNG plant by reducing compressor recycle power. This can result in a large temperature rise in the bed by reducing the inlet temperature of the large methanator and also reducing the exit temperature of the large methanator. This means that more heat of reaction can be used to increase the bed temperature. This results in less heat mass gas being required to absorb the heat released by the reaction and thus a lower recycle flow rate.

The nickel-based catalyst used in U.S. Patent 4,298,694 does not operate stably below about 320 °C. Therefore, to reduce the inlet temperature of the methanator, a shift catalyst comprising at least two of copper, zinc, and chromium is placed on the methanation catalyst. This performs a partial conversion of the feed gas at low temperatures. The exothermic shift reaction is used to preheat the feed to the methanation catalyst and to reduce the amount of conversion that occurs by the high temperature methanation catalyst. The total load of the reactor is similar whether or not there is a shift catalyst. However, its presence makes the temperature entering the reactor lower.

Thus, loading the shift catalyst at the top of the methanation catalyst has a significant impact on reducing the recycle flow rate and ultimately reducing the energy requirements of the recycle compressor because of the higher allowable temperature rise of the combined catalyst bed.

While the initial implementation of the process provides various advantages, the methanation catalyst is typically used at elevated temperatures of from about 500 ° C to about 800 ° C and the shift catalyst is used at lower temperatures of from about 250 ° C to about 350 ° C. Thus, at elevated temperatures, such as at equilibrium temperatures at which the methanation catalyst is operated, the shift catalyst becomes inactive. If the shift catalyst becomes deactivated, the inlet temperature must be raised or the shift catalyst replaced. Increasing the inlet temperature due to shift catalyst deactivation will eliminate the advantages of incorporating the shift catalyst, and when deactivated, catalyst replacement will require costly shutdown of the plant and replacement of the catalyst.

Another method is described in US 2009/0247653. It suggests that the methanation reaction is advantageous at low temperatures and reduced water content. The proposed configuration with two large methanators reduces the temperature of the gas stream at the outlet of the second large methanator to condense some of the water in the stream. The partially dried gas stream is then split between the recycle streams, which are compressed and recycled back to the inlet of the first large methanator, and the stream is passed to a trim methanator.

It is suggested that the method has the advantage of reducing the number of regulated methanators required to achieve the desired product specification, as reducing the number of conditioning methanators tends to reduce plant capital costs. The energy requirements are also slightly saved because of the lower inlet temperature of the recirculating compressor and the lower recirculation rate due to lower water content.

However, in order to prevent carbon deposition on the catalyst in the bulk methanation zone, the water content of the stream exiting the large methanator needs to be minimal. Reducing the temperature entering the recycle compressor reduces the water content in the recycle stream and, therefore, the gas composition exiting the large methanator is in the carbon formation zone.

To prevent carbon from settling on the catalyst, steam is added to the recycle stream upstream of the large methanator. The large amount of steam that needs to be added has an impact on the steam that is discharged from the plant, which significantly affects economic benefits. In addition, the temperature of the stream leaving the large methanator unit is lowered to condense only the water and then reheat the stream and the thermal efficiency of adding water is poor.

Another proposal is indicated in US 2009/0264542. The purpose of the method is to provide a more cost effective method by reducing the power required to recycle the compressor. This is achieved by diverting the carbon oxide-rich feed to a series of large methanators and recycling the product gas from the outlet of the first large methanator back to the inlet of the first large methanator. . Increasing the number of large methanators reduces the required recirculation rate and maintains a pressure differential that is only recirculated around a single large methanator. The combined effect is to reduce the power of the recirculating compressor. Despite the reduced power of the compressor, the capital cost of the plant is increased due to the increased demand for an increased number of expensive refractory lined methanators and associated heat exchangers.

Thus, it can be seen that the basic technology has remained virtually unchanged since the 1970s. The technology has been well understood and in recent years it has been seen that the main recommendations for improvement focus on improving economic efficiency in both capital cost and operating costs. Capital costs are saved by reducing the amount of methanator and catalyst volume needed to produce the desired product. Operating costs are saved by reducing the power requirements of the recirculating compressor and increasing heat recovery. Improved heat recovery increases steam emissions from the plant and thus improves plant economics.

Although some proposals have succeeded in reducing plant operating costs, they have substantially increased their capital costs. Other proposals have reduced capital costs but increased operating costs.

Accordingly, there is a need for a method that reduces operating costs, particularly in terms of recirculating compressor size and power, without significantly increasing the amount of catalyst required and the number of reactors, and preferably also having lower capital costs.

It has been found that if the feed fed to the first and/or second and/or subsequent large methanators is cooled by a recycle gas that has undergone a reaction to regulate and/or recycle the large methanator, Improved methods can be provided.

Accordingly, in accordance with the present invention, there is provided a method of making an alternative natural gas comprising: providing a feed gas to a first and/or second and/or subsequent large methanator; and subjecting the feed gas to the presence of a suitable catalyst a methanation reaction; removing at least a portion of the reaction stream from the first large methanator and providing to a second and/or subsequent large methanator for further methanation; from the last large methanator The product flows into a conditioning methanator where it is further subjected to a methanation reaction; the recycle stream is removed downstream of the first, second or subsequent large methanator and flows through the compressor in any order, undergoes cooling, and then provides The methanator is adjusted and/or recycled for further methanation and then recycled to the first and/or second and/or subsequent methanators.

Recirculation is typically added to the first and/or second and/or subsequent large methanators via introduction to its feed line. However, it can be added directly to a large methanator with individual feed lines.

In a first embodiment of the invention, the method comprises: providing a feed gas to the first and second large methanators; subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; from the first large methanator Removing at least a portion of the reaction stream and providing to a second large methanator for further methanation reaction; removing the gas stream from the second methanator and cooling the stream; splitting the cooling gas stream and Providing a portion to the regulated methanator train, further performing a methanation reaction therein, and providing a portion to the recycle stream; passing the recycle into the compressor; and causing the compression from the compressor to flow into Recirculating the methanator operating at a lower outlet temperature than the first and second large methanators and subjecting the compressed stream to further methanation; and recycling the stream from the recycle methanator to the first / or the second large methanator.

The method of this first embodiment reduces the power requirements of the recirculating compressor. Without being bound by any theory, there are two factors that control the power of the recirculating compressor. It is the recirculation flow rate and the pressure differential across the recirculating compressor. The method of this first embodiment reduces the recycle flow rate by further methanating the recycle stream, thereby increasing the methane content of the stream and reducing the carbon monoxide content of the stream. The amount of methanation carried out in the recycle methanator can be removed from the large methanator load.

The conditioning methanator train can include one or more conditioning methanators. When more than one conditioning methanator is present, it is typically arranged in series. When more than one conditioning methanator is used, it can be operated at the same temperature or the temperature of the second and any subsequent conditioning methanators can be lower than the temperature of the first conditioning methanator. When there are multiple conditioning methanators, the temperature of each subsequent conditioning methanator is lower than the temperature of the previous methanator.

In one configuration of this embodiment, the second recycle stream can be removed from the stream exiting the or first conditioning methanator or subsequent methanator, the regulated recycle stream being provided to the compressor prior to being Combined with a recycle stream from a second and/or subsequent large methanator. In another configuration, the recycle stream may be taken from other regulated methanators in the regulated methanator train or may be taken from a regulated methanator other than the first regulator methanator.

The feed gas portions fed to the first large methanator and the second and/or subsequent large methanators may be the same or different. In a configuration with two large methanators, about 40% of the new feed is fed to the first large methanator and the remainder is fed to the second large methanator. However, it should be understood that the split between the various large methanators will depend on the number of large methanators, operating conditions, and feed composition.

The first and second large methanators can be operated under any suitable reaction conditions. Suitable reaction temperatures include from about 250 ° C to about 700 ° C inclusive.

The first conditioning methanator can operate at a lower temperature than a large methanator.

The recycle methanator can operate at lower temperatures than large methanators. Suitable reaction temperatures include from about 220 ° C to about 550 ° C inclusive.

In general, the outlet temperature of the recycle and conditioning methanator will be lower than the outlet temperature that provides feed to the recycle or adjust the methanator upstream of the methanator.

Since the recycle methanator operates at a lower outlet temperature than the large methanator, a high ratio of residual carbon monoxide and hydrogen in the recycle stream can be converted to methane. The reaction loading carried out by the recycle methanator reduces the load from the large methanation zone. A lower large methanation load results in a lower recycle flow rate.

Although a recycle methanator has been described as an individual methanator, it should be understood that if recycle is to be added therein, the recycle methanator can be located as a stage to accommodate the first large methanator and/or second and / Or in the container of a large-scale methanator. In this configuration, the feed will be added between the reactor portion where the recycle methanation occurs and the large methanator. The method can be arranged to change the feed inlet position when the catalyst is deactivated. In one configuration, the flow direction can be reversed such that the catalyst bed as a recycle methanator becomes the large methanator and the catalyst bed as a large methanator becomes a recycle methanator.

The recirculating methanator is placed in comparison to prior art methods such as those described in US 4,133, 825, in which two large methanation stages are used and the recycle is taken from the second stage outlet and then returned to the upstream of the first stage. The energy consumption of the recirculating compressor can be reduced by 4 to 5% in the recirculation loop.

In prior art methods, two sets of two large methanators in parallel can be used because of container shipping restrictions. The method of the present invention reduces the number of methanators required by the plant and reduces the size of equipment in the loop, which results in a reduction in total capital cost. Large methanator sizes and/or loop conduits are often a factor in determining the number of strings required for a total composite. The incorporation of a recirculating methanator reduces the amount of loop processing and correspondingly reduces the size of large methanators and loop conduits. The recycle methanator has the potential to reduce the number of strings required in the total complex, which will more significantly reduce the total capital cost.

It is understood that the addition of a recycle methanator, associated heat exchangers and lines will increase the pressure drop in the recirculation loop. However, the pressure ratio is only slightly increased and a reduction in recirculating compressor power is produced when compared to saving the recirculation flow rate.

In a second embodiment, the method comprises: providing a feed gas to the first and second large methanators; subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; moving from the first large methanator Dividing at least a portion of the reaction stream and providing to a second large methanator for further methanation reaction; removing the gas stream from the second large methanator and cooling the stream; providing the cooling gas stream to the conditioning a methanator in which a methanation reaction is further carried out, the conditioning methanator operating at a lower outlet temperature than the large methanator; the partial flow from the product stream regulating the methanator and providing a portion thereof to subsequent adjustment The methanator is in series and supplied to the recycle stream; the recycle is passed to the compressor; and the stream is recycled to the first and/or second large methanator.

This is a change to the first embodiment above. This method also serves to reduce the power requirements of the recirculating compressor. In this configuration, the recycle flow rate is reduced by removing the recycle downstream of the conditioning methanator rather than upstream thereof. The methanation reaction is further carried out from the stream exiting the methanator, which thereby increases the methane content of the stream and reduces the amount of carbon monoxide in the stream.

The conditioning methanator can be one or more regulated methanators in series. When more than one conditioning methanator is present, the recycle stream can be taken after any conditioning methanator. The subsequent adjustment of the methanator train can include one or more conditioning methanators. These are generally arranged in series. Subsequent adjustment of the methanator temperature can be lower than the temperature of the first conditioning methanator. When multiple conditioning methanators are present, each methanator can be operated at a lower temperature than its previous conditioning methanator.

In this second embodiment, the overall overall methanation load is reduced because part of it has already been performed in a regulated methanator that has taken out the recycle stream. Thus, such conventional methods as described in U.S. Patent 4,133,825 require a lower recycle flow rate. This method also requires less equipment items added to the recirculation loop, which will result in a lower differential pressure through the compressor than the first embodiment described above at the same flow rate.

Another advantage of this embodiment of the invention is that because the methanation reaction is carried out upstream of the compressor, the number of gas moles can be greatly reduced and thus the volumetric flow rate through the compressor can be greatly reduced. Therefore, the power and the pumping volume ratio of the compressor size are set to be lower than those required in the first preferred embodiment described above. The catalyst volume generally remains the same compared to prior art systems. Operating costs are reduced, but without increasing capital costs.

The first mode of methanator is taken from the prior art as described in US 4,133,825, in which two large methanation stages are used and the recycle is taken from the second stage outlet and then returned to the upstream of the first stage. The downstream recycle stream reduces the power consumption of the recycle compressor by 21 to 22%. This can be achieved by greatly reducing the volumetric flow rate of the compressor pumping. The reduction in large methanator load can reduce the number of methanators required compared to prior art methods.

In one configuration of this embodiment, the second recycle stream can be taken between the second large methanator and the conditioning methanator.

If desired, the recycle methanator can be incorporated into the recycler and the recycle stream that introduces the recycle stream between the first and/or second and/or subsequent large methanators. As described above in connection with the first embodiment of the invention, the recycle methanator can be located as a zone in the same vessel as the first large methanator or any large methanator to be introduced into the recycle stream.

Methanation of the recycle stream in the conditioning methanator and subsequent introduction to the compressor will substantially reduce the number of moles that the compressor must be compressed to achieve the heat dissipation required by the large methanator, and thus reduce power consumption.

When the recycle methanator is present in the recycle loop, more than one recycle methanator can be used.

In a third embodiment, the method comprises: providing a feed gas to the first and second large methanators; subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; moving from the first large methanator In addition to at least a portion of the reaction stream and provided to a second large methanator, wherein the methanation reaction is further carried out; the gas stream is removed from the second methanator and the stream is cooled; at least a portion of the cooling is passed into compression Providing the compressed stream to a recycle methanator for further methanation reaction; diverting the product stream from the recycle methanator and flowing a portion thereof to the conditioning methanator for further A methanation reaction is carried out; the remainder of the product stream is recycled to the first and/or second large methanator.

This configuration is a variation of the first embodiment described above. Although the power requirements of the recirculating compressor are not reduced in this configuration, they result in a reduction in the total number of equipment for the flow chart and thus a reduction in overall capital cost. In this embodiment, the stream exiting the recycle methanator has undergone compression and further methanation reactions as discussed above with respect to the first embodiment.

This third embodiment can be used to reduce the effective total pressure drop of the methanation unit without adding expensive equipment items, such as additional compressors or additional methanation stages (which would be required to pressurize the methanation gas). The configuration of this embodiment also utilizes the advantage of adjusting the methanation zone under boost operation, which will drive equilibrium to produce more methane under the same temperature conditions.

In the above method, the portions of the feed gas fed to the first large methanator and the second large methanator may be the same or different. In one configuration with two large methanators, about 40% of the fresh feed gas is fed to the first large methanator and the remainder is fed to the second large methanator. However, it should be understood that the feed split between the methanators will depend on the amount of large methanator, operating conditions, and feed composition.

Features described in connection with the first or second embodiment described above may be suitably combined with this embodiment.

Although the above method has been described with reference to the presence of two large methanators, it should be understood that in some cases it may be desirable to use more than two large methanators. In this configuration, the recycle will generally be taken downstream of the last large methanator, and the recycle stream that has passed through the reactor and compressor in any order will be recycled to one or more large methanation if appropriate. In the device.

The feed to the large methanator can be stoichiometric or non-stoichiometric.

In any embodiment of the invention, water can be removed from the recycle stream. When water is to be removed, it is usually removed before it is recycled into the compressor. In general, for some feed compositions and operating conditions, only water needs to be removed.

In one configuration of any of the preferred embodiments of the present invention, the feed from the first large methanator to the second large methanator can flow through the catalyst bed, which is located above and above the catalyst bed The overall methanation reaction is higher than where the feed is added to the vessel. The stream exiting the first large methanator is then subjected to a conditioning methanation reaction prior to mixing with the new feed and performing an overall methanation reaction.

The shift reaction is typically carried out before the feed is provided to the large methanator, but in another configuration, the shift reaction can be carried out in a large methanator.

Two preferred embodiments of the present invention reduce overall plant operating costs by reducing recirculating compressor power.

For the process of the present invention, it is possible to move more catalyst from the large methanator to the conditioning methanator, which is advantageous because the catalyst life is generally longer and the lower temperature can be lowered due to reduced poisoning. Sintering risk.

Regardless of which embodiment of the invention is used, a small amount of steam is preferably added upstream of the recycle stream of the overall methanation reaction stage to prevent carbon from settling on the catalyst. However, even when present, this flow rate is relatively small compared to the overall steam production in a large methanator and is generally less than 5% of the total steam produced.

In one configuration, steam can be introduced into the system stream via a feed saturator disposed upstream of the large methanator. Therefore, steam can be added without directly adding steam.

With regard to the methanation reaction, the new feed fed to the first and/or second and/or subsequent large methanators can be stoichiometric or non-stoichiometric.

The invention will be described by way of example with reference to the accompanying drawings.

Those skilled in the art will appreciate that such drawings are diagrammatic and that commercial plants may require other equipment items such as feed drums, pumps, vacuum pumps, compressors, gas recirculation compressors, temperature sensors, pressure sensors, Pressure relief valve, control valve, flow controller, liquid level controller, storage tank, storage tank, etc. The provision of such equipment does not form part of the present invention and is in accordance with conventional chemical engineering practices.

One embodiment of the invention is described in FIG. The carbon monoxide-rich desulfurization feed gas is fed into line 1 into an overall methanation zone consisting of two large methanators (the first large methanator 2 and the second large methanator 3). Thus, the feed split, a portion of which is fed into line 1a, into the first large methanator 2, and a portion of which enters the second large methanator 3 via line 1b. The product from the first large methanator 2 flows into line 4 and into the second large methanator 3. It is usually cooled in the heat exchanger 5 and then added to the second large methanator 3.

The product from the second large methanator 3 flows into line 6 into heat exchanger 7 where it is cooled. A portion from the heat exchanger flows into line 8 into the first conditioning methanator 9. The remaining flow-through line 10 from the heat exchanger 7 enters the compressor 13 via the heat exchanger 11 and the line 12. In the heat exchanger 11, the recycle stream is cooled and then compressed in the compressor 13.

The gas from the compressor is passed to line 14 via a heat exchanger 15 and line 16 heated to a recirculating methanation operating temperature to a recycle methanator 17, where the methanation reaction is further carried out. The gas from the recycle methanator is removed from the recycle methanator in line 18, passed through heat exchanger 19 and returned to first large methanator 2 via line 20. In general, returning to the first large methanator 2 is through the feed line 1a.

The product from the conditioning methanator 9 is removed in line 21 and passed through heat exchanger 22 where it is cooled. It then flows into line 23 into one or more subsequent conditioning methanators 24. The product is withdrawn in line 25 and subsequently cooled and dried in cooler/dryer 26. The SNG is then removed in line 27.

In one embodiment, the large methanator can be operated such that the feed to which it is added is at about 320 °C. After the reaction and heat exchange, the feed to the first conditioning methanator 9 is at about 280 °C. The feed to the recycle methanator 17 is also about 280 °C. The feed to the subsequent adjustment methanator 24 is typically about 250 °C.

In the flow chart shown in Figure 1, the portion of the stream removed from the first conditioning methanator 9 is added to line 28 to the recycle stream feed to compressor 13 and thus to the recycled methane. In the chemist 17 .

Depending on the feed composition and operating conditions, water may need to be removed or better. This is preferably done in line 29 prior to the compressor.

A stream can be added to line 30. This is only required for some feed compositions and operating conditions.

A second embodiment of the invention is described in FIG. The carbon monoxide-rich desulfurization feed gas is fed to line 31 into an overall methanation zone comprised of two large methanators (the first large methanator 32 and the second large methanator 33). Therefore, the feed splits, a part of which is fed into the line 31a, It enters the first large methanator 32 and a portion enters the second large methanator 33 via line 31b. The product from the first large methanator 32 flows into line 34 and into the second large methanator 33. It is typically cooled in heat exchanger 35 and then added to second large methanator 33.

The product from the second large methanator 33 flows into line 36 into heat exchanger 37 where it is cooled. The flow-through line 38 from the heat exchanger 37 enters the first conditioning methanator 39. After methanation in the conditioning methanator 39, the stream is removed in line 40, with a portion of it flowing into line 41, via heat exchanger 42 and line 43, into compressor 44. In heat exchanger 42, the recycle stream is cooled to achieve the desired steam to carbon ratio in the overall methanation zone. Because the stream taken from the conditioning methanator 39 has been further methanated and at a lower temperature, it has a lower carbon monoxide and hydrogen content and a higher methane content than the gas exiting the second large methanator 33.

Gas from the compressor is passed to line 45, via heat exchanger 46, where it is heated and then passed through line 47 to the large methanator 32. In general, returning to the first large methanator 32 is via feed line 31a.

The portion of the stream from the conditioning methanator 39 that is not passed to the compressor 44 is removed in line 48 and passed through heat exchanger 49 where it is cooled. It then flows into line 50 into one or more subsequent conditioning methanators 51. The product is withdrawn in line 52 and then cooled and dried in a cooler/dryer 53. The SNG is then removed in line 54.

In one embodiment, the large methanator can be operated such that the feed fed thereto is at about 320 °C. After the reaction and subsequent heat exchange, the feed to the first conditioning methanator 39 is at about 280 °C. The feed to the subsequent adjustment methanator 51 is typically about 250 °C.

In the flow chart shown in FIG. 2, a portion of the stream removed from the heat exchanger 37 and bypassing the first conditioning methanator 39 can be added to the recycle stream fed to the compressor 44 in line 55 and It thus enters the large methanator 32.

Depending on the feed composition and operating conditions, water may need to be removed or removed. This is preferably done in line 56 prior to compressor 44.

A stream can be added in line 57. This is only required for some feed compositions and operating conditions.

Recirculating methanator 58 and subsequent heat exchanger 59 may be located after compressor 44 in the recirculation loop, as desired.

In one embodiment of this embodiment, the large methanator can be operated such that the feed fed thereto is at about 320 °C. After the reaction and subsequent heat exchange, the feed to the first conditioning methanator 39 is at about 280 °C. The feed to the recycle methanator 58 (if present) is also about 280 °C. The feed to the subsequent adjustment methanator 51 is typically about 250 °C.

If desired, the recycle methanator (if present) can be combined in the same vessel as the large methanator to be fed to the recycle stream. This is shown schematically in Figure 3. The configuration illustrated in Figure 3 also includes the possibility that the second large methanator also has a reactor for methanating the cooling gas located on the upper portion of the vessel. However, it should be understood that the two configurations may be used alone or in combination.

As shown in Figure 3, a new feed is fed into line 100. It is split and fed into containers 101 and 102 via lines 103 and 104, respectively. Container 101 includes two reaction zones 105 and 106 and adds feed between the two zones. Because of the downward flow, the feed added to line 103 will flow through reaction zone 106 where it contacts the methanation catalyst at the desired temperature for bulk methanation.

Recirculation from the compressor (not shown in this figure) is added to vessel 101 in line 107. It flows down through reaction zone 105, which acts as a recycle methanator and undergoes a methanation reaction, which is then mixed with the gas feed added in line 103.

The product from the bulk methanation reaction is removed in line 108 and passed to heat exchanger 109 where it is cooled and then passed to a second large methanator. This can be a conventional large methanator or can be the container 102 shown in FIG. In this configuration, a stream from the first large methanator is added to line 110 to the top of the vessel where it flows through catalyst bed 111 and undergoes a methanation reaction, which is then mixed with the new feed added to line 104. Reflow to the catalyst bed 112 where an overall methanation reaction occurs. The product is then removed in line 113 prior to the removal process in accordance with the present invention.

Another configuration of the present invention is illustrated in FIG. The carbon monoxide-rich desulfurization feed gas is fed to line 201 into an overall methanation zone comprised of two large methanators (the first large methanator 202 and the second large methanator 203). Thus, the feed split, a portion of which is fed into line 201a, into the first large methanator 202, and a portion into the second large methanator 203 via line 201b. As described below, it is not fed directly into the second large methanator 203, but is first mixed with the product stream from the first methanator 202.

The product from the first large methanator 202 flows into line 204 and enters heat exchanger 205 where it is cooled. It then passes into line 206 and into the second large methanator 203. The stream is mixed with the feed added to line 201b prior to addition to the methanator.

The product from the second large methanator 203 flows into line 207 into heat exchanger 208 where it is cooled. A portion from the heat exchanger flows into line 209 and enters compressor 210 where it is compressed. The gas from the compressor is passed to line 211, into heater 212 where it is heated to the recirculation methanation operating temperature and then passed to line 213 where it is passed to a recycle methanator 214 where it is further subjected to a methanation reaction.

The product stream from recycle methanator 214 is removed in line 215 and passed to cooler 216. The cooling stream is removed in line 217 and then split into lines 218 and 219. A portion of line 218 is recycled to first methanator 202. The cooling stream portion of line 219 flows to first conditioning methanator 220. Product from the first conditioning methanator 220 passes into line 221 and enters cooler 222. Cooling then flows into line 223, into second conditioning methanator 224, and then into line 225, into dryer 226. The SNG is then removed in line 227.

The invention will now be described with reference to the following examples.

Comparative Example A

This "basic example" flow diagram has two large methanators in the recycle loop and is followed by a two-stage adjustment of the methanation reaction that is not included in the recycle loop. The flow chart uses a stoichiometric feed and is designed to produce a product comprising 96% methane. Table 1 summarizes the main operating parameters of the flow chart and lists details of the recycle flow, loop pressure drop, and expected compressor power for this example.

Example A1

The recycle methanator has been added to the loop downstream of the recycle compressor. The other two heat exchangers are also added to the recirculation loop, the first for heating the feed to the recirculating methanator to the correct temperature and the second for cooling the recirculating methanator product. The flow chart is also designed to produce a product containing 96% methane. Table 2 summarizes the main operating parameters of the flow chart and lists the details of the recycle flow, loop pressure drop, and expected compressor power for this example.

This example shows that, despite the addition of the recycle methanator and associated heat exchanger to the recirculation loop, the overall compressor power of this example is about 5% lower than the basic example flow chart. Since some of the methanation loading typically occurring in large methanators has been transferred to the recycle methanator, there is a significant reduction in the rate of recycle required to control the temperature of the large methanator outlet, resulting in improved compressor power.

Example A2

In this example, there is no methanator or other equipment item added to the flow chart, but at the point of recirculation removal has moved from the outlet of the large methanator 2 to the outlet of the conditioning methanator 1, ie The conditioning methanator 1 is now incorporated into the recirculation loop. Another conditioning methanator (conditioning methanator 2) was incorporated outside of the recycle loop to obtain the same number of large methanators and to adjust the total number of methanators as in the comparative example. The flow chart was designed to produce a product containing 96% methane. Table 3 summarizes the main operating parameters of the flow chart and lists the details of the recycle flow, loop pressure drop, and expected compressor power for this example.

This example shows that, although the conditioning methanator 1 is incorporated into the recycle, the overall compressor power of this example is about 20% lower than the flow chart of the basic example. This example also shows a significant improvement over Example A1. Since the overall methanation reaction load in the recirculating methanator flow diagram of Example A1 has been reduced (at this time, since part of it has been performed in the conditioning methanator 1). The bulk methanation zone in turn requires a lower recycle flow rate than the flow chart of Comparative Example A. Moreover, as an improvement to the design of Example A1, fewer equipment items were added to the loop, which resulted in a lower pressure differential across the recirculating compressor. Another major advantage of this configuration is that the methanation reaction in the conditioning methanator 1 is carried out upstream of the compressor, so that the gas mole number and thus the volumetric flow rate into the compressor is greatly reduced (3H ₂ +CO→CH ₄ +H ₂ O). Therefore, the power and pumping volume of the design (which sets the compressor size) are lower than those of Comparative Example A and Example A1.

Comparative Example B

The "Basic" flow diagram has two large methanators in the recycle loop and is followed by a two-stage adjustment of the methanation reaction in the recycle loop. The flowchart of a non-stoichiometric, and the carbon-rich feed designed to produce a product containing 97.5% methane after removal downstream OSBL CO _2. Table 4 summarizes the main operating parameters of the flow chart and lists the details of the recycle flow, loop pressure drop, and expected compressor power for this example.

real Example B1

A recycle methanator has been added to the recycle compressor downstream of the loop. Another heat exchanger is also added to the recycle loop to cool the recycle methanator product. However, the addition of the unit allows the heat exchanger upstream of the loop to be removed, with the result that the loop and product are at a higher pressure. The flow chart was also designed to produce a product containing 97.5% methane. Table 5 summarizes the main operating parameters of the flow chart and lists details of the recycle flow, loop pressure drop, and expected compressor power for this example.

This example shows that, despite the addition of the recycle methanator and associated heat exchanger to the recirculation loop, the overall compressor power of this example is about 7% lower than the basic example flow chart. As in Example A1, some of the methanation loading typically occurring in large methanators has been transferred to the recycle methanator, requiring a significant reduction in the recycle rate to control the exit temperature of the large methanator, resulting in improved compressor power.

Example B2

In this example, there are no methanators or other equipment items that are additionally added to or removed from the flowchart. However, the point of recycle removal moves from the outlet of the large methanator 2 to the outlet of the conditioning methanator 1, ie the conditioning methanator 1 is now incorporated into the recirculation loop. The modulating methanator 2 is contained outside the recirculation loop to obtain the same number of large methanators and the total number of methanators. The flow chart was designed to produce a product containing 97.5% methane. Table 6 summarizes the main operating parameters of the flow chart and lists the details of the recycle stream, loop pressure drop, and expected compressor power for this example.

This example shows that, although the conditioning methanator 1 is incorporated into the recirculation loop, the overall compressor power of this example is about 10% lower than the basic example flow chart. This example also shows an improvement over Example B1. Furthermore, because in Example A2, the recycle methanator flow diagram, the overall bulk methanation reaction load has been reduced (at this time, since it is partially carried out in the conditioning methanator 1). The overall methanation zone therefore required a lower recycle flow rate than the flow chart of Comparative Example B.

As with Example A2, another major advantage of this configuration is that the methanation reaction in the conditioning methanator 1 is carried out upstream of the compressor, so that the gas mole number and thus the volume flow rate into the compressor is greatly reduced (3H ₂ + CO→CH ₄ +H ₂ O). Therefore, the design power and pumping volume (which sets the compressor size) are lower than in Comparative Example B and Example B1.

Comparative Example C

This flow scheme uses a approaching stoichiometric feed and is designed to produce a product comprising 96% methane as in Example A1. The flow chart has been altered to include all of the recycle stream via the recycle methanator. Table 7 summarizes the main operating parameters of the flow chart and lists the details of the recycle stream, loop pressure drop, and expected compressor power for this example.

This example shows that since the recycle methanator and associated heat exchanger are added to the recirculation loop and all of the recycle stream enters the compressor, the overall compressor power of this example is higher than the basic example flow chart. However, this example demonstrates that product pressure and methane content can be increased without adding any excess equipment items.

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Figure 1 is a block flow diagram of a first embodiment of the present invention;

Figure 2 is a block flow diagram of a second embodiment of the present invention;

Figure 3 is a schematic representation of a configuration in which a recycle methanator is combined in the same vessel as the first large methanator;

Figure 4 is a schematic representation of a third embodiment of the present invention.

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Claims (8)

A method of preparing an alternative natural gas, comprising: supplying a feed gas to a first and/or second and/or subsequent large methanator; and subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; A large methanator removes at least a portion of the reaction stream and provides it to the second and/or subsequent large methanator for further methanation therein; the product from the last large methanator is passed to Regulating the methanator train in which the methanation reaction is further carried out; removing the recycle stream downstream of the first, second or subsequent large methanator and flowing it through the compressor in any order, undergoing cooling, and then It is provided to a recycle methanator for further methanation and then recycled to the first and/or second and/or subsequent methanators. The method of claim 1, wherein the method comprises: providing a feed gas to the first and second large methanators; and subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; from the first large methanator Removing at least a portion of the reaction stream and providing it to the second large methanator for further methanation reaction; removing the gas stream from the second large methanator and cooling the stream; The cooling gas stream is split and a portion is supplied to the regulator methanator train for further methanation and a portion is provided To the recycle stream; circulating the recycle to the compressor; flowing the compression from the compressor to a recycle methanator operating at a lower outlet temperature than the first and second large methanators, and The compressed stream is further subjected to a methanation reaction; and the stream is recycled from the recycle methanator to the first and/or second large methanator. The method of claim 2, wherein the second recycle stream is removed from the subsequent stream of methanator. The method of claim 2 or 3, wherein the recycle methanator is configured to receive a zone in the vessel of the first large methanator and/or the second large methanator. The method of claim 1, comprising: providing a feed gas to the first and second large methanators; and subjecting the feed gas to a methanation reaction in the presence of a suitable catalyst; from the first large methanator Removing at least a portion of the reaction stream and providing it to the second large methanator for further methanation reaction; removing the gas stream from the second large methanator and cooling the stream; at least one Part of the cooling is circulated to the compressor; the compressed stream is supplied to a recycle methanator where a further methanation reaction is carried out; the product stream from the recycle methanator is split and partially The methanator is passed to a series of methanators for further methanation; the remainder of the product stream is recycled to the first and/or second large methanator. The method of any one of claims 1 to 3 and 5, wherein water is removed from the recycle stream. The method of any one of claims 1 to 3, wherein the feed from the first large methanator to the second and/or subsequent large methanators flows through a catalyst bed, which is located Above the catalyst bed where the bulk methanation reaction takes place and above where the new feed is added to the vessel. The method of any one of claims 1 to 3, wherein the new feed system fed to the first and/or second and/or subsequent large methanators is stoichiometric with respect to the methanation reaction, or Non-stoichiometric.